1. Field of the Invention
The present invention relates to a control system for an automatic transmission and a method thereof. More particularly, the present invention relates to a control system for an automatic transmission and a method thereof that can provide shift-speed control improving acceleration responsiveness by determining a virtual positional change of an accelerator pedal VAPS containing an acceleration intention from a positional change of the accelerator pedal Δ APS due to tip-in and a tip-in speed.
2. Description of Related Art
An automatic transmission includes a friction element, a state of which is changed from engagement to release and another friction element, a state of which is changed from release to engagement according to a shift control of a vehicle. Operations of the friction elements are controlled by hydraulic pressure. In addition, because performance of the automatic transmission is influenced by engagement or release timing of the friction elements, research has been carried out so as to improve shift performance further.
The automatic transmission includes a transmission control unit (TCU) for controlling the shift, and the transmission control unit determines a target shift-speed from a predetermined shift pattern map according to a driving speed and a positional change of an accelerator pedal (throttle valve opening). After the target shift-speed is determined, the transmission control unit controls the hydraulic pressure through an actuator (solenoid valve) such that an on-coming friction element is to be engaged and an off-going friction element is to be released. Therefore, the shift to the target shift-speed is controlled.
Because the predetermined shift pattern map of the automatic transmission is set so as to improve fuel economy, acceleration responsiveness may be deteriorated.
In addition, if the positional change of the accelerator pedal according to tip-in is within a reference range of upshift/downshift of the shift pattern map, the shift is not influenced by the positional change of the accelerator pedal. Therefore, upshift or downshift is not performed and a current shift-speed is maintained.
At this time, engine output rises and vehicle speed increases by the tip-in of the accelerator pedal. Because the shift-speed does not change, the vehicle speed increases only by the engine output and thus acceleration responsiveness may be deteriorated, however.
For example, FIG. 6 illustrates a case where the positional change of the accelerator pedal occurs by the tip-in but the shift-speed does not change in a state of a seventh forward speed. That is, because the positional change of the accelerator pedal is within the reference range of upshift/downshift of the shift pattern map, the shift-speed is maintained to be the seventh forward speed that is a current shift-speed. In this case, the vehicle speed increases due to increase of the engine output.
Since the shift-speed, however, does not change, the vehicle speed changes slowly. Therefore, acceleration responsiveness may be insufficiently provided compared with acceleration intention of a driver according to the tip-in.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.